1. Field of the Invention
This invention relates to tubular composite arc welding electrodes of the type comprising a metallic outer sheath and a core within and enclosed by the sheath. More particularly, the invention relates to such electrodes balanced to produce hard surfacing weld deposits in the open-arc, or self-shielded, welding process in which an improved core composition incorporating prescribed amounts of alloyed forms of at least one of the metals magnesium, calcium, strontium and barium provides spray transfer operation. With use in addition of defined quantities of unalloyed magnesium and aluminum, porosity is minimized or eliminated in deposits produced with our electrodes.
2. Description of the Prior Art
Numerous tubular composite electrodes have been developed by the prior art for use in automatic and semi-automatic electric arc hard surfacing processes; among these are those known as self-shielded electrodes, in which components in the core of the electrode provide arc shielding so that no external shielding source is required during the welding operation.
While self-shielded tubular hard surfacing electrodes of many kinds have been largely successful and widely used, a continuing problem, especially with prior art electrodes producing deposits containing titanium carbide (TiC electrodes), has been that arc transfer with such electrodes is what is known in the art as "globular", an unattractive transfer mode characterized by large balls of molten weld metal dropping from the electrode tip to the molten weld pool. In addition, weld metal from such prior art self-shielded tubular TiC electrodes is undesirably low in fluidity, e.g., showing poor or no tie-in between adjacent beads. The transfer and fluidity problems have limited the practical deposit height with prior art TiC electrodes to two or three layers at most; above that height the globules or balls of transferring metal tend either not to fuse properly with the previously deposited metal or to fly in erratic directions from the electrode tip, frequently not landing on the deposit at all. Globular transfer also appears to have limited the amount of titanium carbide recoverable in deposits from tubular composite TiC electrodes such as those manufactured and sold by Teledyne McKay as TUBE-ALLOY.RTM. 240 TiC-O, 258 TiC-O and 829-0.
Since it is often desirable and even necessary to apply multi-pass and multi-layer surfacing deposits on worn or wear-prone base materials, and since enhanced wear resistance could be achieved with higher TiC levels in deposits bearing such carbides, self-shielded tubular composite hard surfacing electrodes in which the foregoing problems are minimized or eliminated would have significantly broader utility and attractiveness than electrodes heretofore available.